This invention relates to an improved clip for use with transparent conductive metal oxide electrodes in electrochromic devices and, more particularly, to an improved clip comprising a dimple that has high contact stability over long periods of time when in contact with a metal oxide film, even when operated at low voltages and low currents.
Heretofore, various automatic rearview mirrors for motor vehicles have been devised which automatically change from the full reflectance mode (day) to the partial reflectance mode(s) (night) for glare protection purposes from light emanating from the headlights of vehicles approaching from the rear. The electrochromic mirrors disclosed in U.S. Pat. No. 4,902,108, entitled "Single-Compartment, Self-Erasing, Solution-Phase Electrochromic Devices Solutions for Use Therein, and Uses Thereof", issued Feb. 20, 1990, to H. J. Byker; Canadian Patent No. 1,300,945, entitled "Automatic Rearview Mirror System for Automotive Vehicles", issued May 19, 1992, to J. H. Bechtel, et al.; U.S. Pat. No. 5,128,799, entitled "Variable Reflectance Motor Vehicle Mirror"issued Jul. 7, 1992, to H. J. Byker; U.S. Pat. No. 5,202,787, entitled "Electro-Optic Device" issued Apr. 13, 1993, to H. J. Byker, et al.; U.S. Pat. No. 5,204,778, entitled "Control System For Automatic Rearview Mirrors", issued Apr. 20, 1993, to J. H. Bechtel; U.S. Pat. No. 5,278,693, entitled "Tinted Solution-Phase Electrochromnic Mirrors", issued Jan. 11, 1994, to D. A. Theiste, et al.; U.S. Pat. No. 5,280,380, entitled "UV-Stabilized Compositions and Methods", issued Jan. 18, 1994, to H. J. Byker; U.S. Pat. No. 5,282,077, entitled "Variable Reflectance Mirror", issued Jan. 25, 1994, to H. J. Byker; U.S. Pat. No. 5,294,376, entitled "Bipyridinium Salt Solutions", issued Mar. 15, 1994, to H. J. Byker; U.S. Pat. No. 5,336,448, entitled "Electrochromic Devices with Bipyridinium Salt Solutions", issued Aug. 9, 1994, to H. J. Byker; U.S. Pat. No. 5,434,407, entitled "Automatic Rearview Mirror Incorporating Light Pipe", issued Jan. 18, 1995, to F. T. Bauer, et al.; U.S. Pat. No. 5,448,397, entitled "Outside Automatic Rearview Mirror for Automotive Vehicles", issued Sep. 5, 1995, to W. L. Tonar; and U.S. Pat. No. 5,451,822, entitled "Electronic Control System", issued Sep. 19, 1995, to J. H. Bechtel, et al., each of which patents is assigned to the assignee of the present invention and the disclosures of each of which are hereby incorporated herein by reference, are typical of modern day automatic rearview mirrors for motor vehicles. Such electrochromic mirrors may be utilized in a fully integrated inside/outside rearview mirror system or as an inside or an outside rearview mirror system. In general, in automatic rearview mirrors of the types disclosed in the above-referenced U.S. and Canadian Patents, both the inside and the outside rearview mirrors are comprised of a relatively thin electrochromic medium sandwiched and sealed between two glass elements.
In most cases, when the electrochromic medium which functions as the media of variable transmittance in the mirrors is electrically energized, it darkens and begins to absorb light, and the more light the electrochromic medium absorbs the darker or lower in reflectance the mirror becomes. When the electrical voltage is decreased to zero, the mirror returns to its clear high reflectance state. In general, the electrochromic medium sandwiched and sealed between the two glass elements is comprised of solution-phase, self-erasing system of electrochromic materials, although other electrochromic media may be utilized, including an approach wherein a tungsten oxide electrochromic layer is coated on one electrode with a solution containing a redox active material to provide the counter electrode reaction. When operated automatically, the rearview mirrors of the indicated character generally incorporate light-sensing electronic circuitry which is effective to change the mirrors to the dimmed reflectance modes when glare is detected, the sandwiched electrochromic medium being activated anid the mirror being dimmed in proportion to the amount of glare that is detected. As glare subsides, the mirror automatically returns to its normal high reflectance state without any action being required on the part of the driver of the vehicle.
The electrochromic windows of the invention have similar construction and operation as the electrochromic mirrors of the invention except that the size or area can be much larger and a reflector layer is not needed.
For mirrors the electrochromic medium is disposed in a sealed chamber defined by a transparent front glass element, a peripheral edge seal, and a rear mirror element having a reflective layer. Conductive layers are provided on the inside of the front and rear glass elements, the conductive layer on the front glass element being transparent while the conductive layer on the rear glass element may be transparent or may be semi-transparent or opaque and may also have reflective characteristics and function as the reflective layer for the mirror assembly. The conductive layers on both the front glass element and the rear glass element are connected through clips to electronic circuitry which is effective to electrically energize the electrochromic medium to switch the mirror to nighttime, decreased reflectance modes when glare is detected and thereafter allow the mirror to return to the daytime, high reflectance mode when the glare subsides as described in detail in the aforementioned Patents. For clarity of description of such a structure, the front surface of the front glass element is sometimes referred to as the first surface, and the inside surface of the front glass element is sometimes referred to as the second surface. The inside surface of the rear glass element is sometimes referred to as the third surface, and the back surface of the rear glass element is sometimes referred to as the fourth surface.
Conductive clips are used to impart a potential from a power supply to the conductive materials. The vast majority of prior art clips used in the electronics industry, however, are designed to provide adequate electrical contact to metals. Typically a stable electrical contact is maintained during wiping contact where there is repeated opening and closing of the point of contact between the clip and the metal, or where the high current or voltage "burns " through any oxides that are formed on the metal.
A prior art, ribbed, clip 10 used to contact metaI oxides is shown in FIG. 1 and is generally "U " shaped having a grooved back 12 and two sides (14 and 16). Recesses (18 and 20) are disposed in the sides to allow for flexibility and a rib or groove 13 is formed in the back to provide some stiffness and rigidity to the clip 10. These prior art clips exhibit a steep rise in contact resistance over time because of poor contact stability with the transparent conductors within electrochromic devices. This is especially true for low cost atmospheric applied CVD coatings, such as LOF Tech glass where the metal oxide surface is hard and very rough. This rise in contact resistance causes a deterioration in the performance of an electrochromic device by decreasing coloring speed and coloring uniformity and, for electrochromic mirrors, decreasing low end reflectivity. These poor connections typically do not cause catastrophic failures because there is so much redundancy due to the many points of contact around the periphery of an electrochromic device. Most automotive electrochromic mirrors produced today are interior mirrors wherein the clips are not exposed directly to moisture or corrosive road salt environments. Most outside electrochromic mirror assemblies in production today incorporate a means for sealing or protecting the clip from direct exposure to moisture or salt spray by potting the clips in a polymer or adhesive (see, for example, U.S. Pat. No. 5,448,397, entitled "Outside Automatic Rearview Mirror for Automotive Vehicles " to W. L. Tonar et al.), or creating a sealed chamber (see, for example, U.S. patent application Ser. No. 5,216,536, entitled "Encapsulated Electrochromic Device and Method for Making Same " to A. Agrawal et al.). Further, because the lifetime of the only commercially available electrochromic devices (eyeglasses and automobile mirrors) does not extend much past 10 years, this redundancy has eliminated any catastrophic failures. However, as electrochromic windows become available (whose lifetime must be 20-30 years), these poor electrical connections become much more important. One reason for this is that for a large window to color evenly, there must be good contact all around the periphery and if a portion of the individual connections fail, then the window will color unevenly which is very aesthetically displeasing to consumers. It is also desirable to have designs where clip protection by potting in a polymer or adhesive or creating a sealed chamber is not required.
Consequently, it is desirable to provide an improved conductive clip comprising a dimple that has high contact stability over long periods of time when supplying potential to at least one transparent conductor within an electrochromic device, even when operated at low voltages and low currents.